Carburetor cold enrichment device

ABSTRACT

A carburetor without a choke valve has a cold enrichment system that adds additional fuel and air to the system for cold weather operation. The added mixture is controlled by a valve that is responsive to engine and ambient temperatures as well as manifold vacuum changes to properly proportion the added mixture.

United States Patent [191 Charron et a1.

[ 1 May 27, 1975 1 1 CARBURETOR COLD ENRICHMENT DEVICE [75] Inventors: William W. Charron, Orchard Lake; William E. Dickensheets, Southfield; Robert S. Harrison, Grosse lle; Alvin P. Nowroslti, Livonia, all of Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: July 2, 1973 21 Appl. No.: 375,973

[52] US. Cl 123/180 R; 123/179 G; 261/39 D [51] Int. Cl. F02m l/06; F02m 1/10 [58] Field of Search..... 123/180 R, 180 T, 179 G,

123/187.5 R; 261/39 B, 39 D, DIG. 8

[56] References Cited UNITED STATES PATENTS 1,696,929 l/1929 Stokes 123/180 T Primary Examiner-Charles .1. Myhre Assistant Examiner-W. Rutledge, Jr.

Attorney, Agent, or FirmRobert E. McCollum; Keith L. Zerschling [5 7] ABSTRACT A carburetor without a choke valve has a cold enrichment system that adds additional fuel and air to the system for cold weather operation. The added mixture is controlled by a valve that is responsive to engine and ambient temperatures as well as manifold vacuum changes to properly proportion the added mixture.

6 Claims, 5 Drawing Figures P/UENTED MAYZ 7 I975 SHEET PATENTED MAY 27 I975 SHEET CARBURETOR COLD ENRICHMENT DEVICE The advent of lower vehicle hoodlines necessitates a i change in engine carburetion design. The prior art carburetor designs of the downdraft type generally include in the induction passage a choke valve located above the fuel metering venturi. This adds height to the carburetor and necessitates either providing a hump in the hood or higher hood profiles.

This invention relates to a carburetor design that eliminates the need for a choke valve and thereby permits decreasing the overall height of the carburetor. The invention compensates for the lack of a choke system by providing a cold enrichment device that adds fuel and air to the carburetor during cold weather operation to supplement that fuel and air normally supplied to the carburetor under warm operating conditions. The conventional choke valve effects an overrich mixture during engine cranking operations, followed by a cracking open of the choke valve to lean the mixture to a less rich but still richer than normal level. The conventional choke valve, therefore, controls the flow of both air and fuel and causes additional fuel to be added to the system during cold weather operation.

The present invention accomplishes the same objectives as a conventional choke valve without'requiring the use of one. i

More particularly, the invention connects an additional conduit from the carburetor fuel reservoir with additional air to a point in the carburetor induction passage downstream of the throttle valve. The flow of extra fuel and air is controlled by a valve movable in response to temperature changes as well as manifold vacuum changes to schedule a desired air/fuel mixture richness corresponding to that normally provided by a conventional choke valve. During cranking of the engine, therefore, an overrich mixture is supplied to the engine. When the manifold vacuum increases above the engine cranking level, the rich mixture is immediately leaned by the valve closing down the added fuel supply somewhat and allowing other means to introduce further heated air to the system. Various tempera ture and vacuum controls automatically schedule the correct proportion of additional fuel and air to the engine until the normal engine operating temperatures are reached, at which point the enrichment device is completely shut off so that the carburetor fuel system then operates in a conventional manner.

It is a primary object of the invention, therefore, to provide a cold enrichment system for an internal combustion engine carburetor to supplement the normal carburetor air/fuel mixture requirements during cold weather engine cranking and running operations.

It is a further object of the invention to provide a cold enrichment device of the type described in which a valve movable by temperature and manifold vacuum controls automatically schedules additional amounts of fuel and airflow to the carburetor in accordance with engine and ambient temperatures.

Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed description thereof, and to the drawings illustrating the preferred embodiment thereof; wherein, v

FIG. 1 is a top or plan view of a carburetor embodying the invention;

FIGS. 10 and 2 are enlarged cross-sectional views taken on planes indicated by and viewed in the direction of the arrows Ia-1a and 2-2, respectively, of FIG. 1; and,

FIGS. 3 and 4 are crosssectional views taken on planes indicated by and viewed in the direction of the arrows 33 and 44, respectively, of FIG. 1.

FIGS. 1 and la show in general a carburetor of the downdraft type on which the cold enrichment device to be described is installed. This particular carburetor is of the variable venturi type. It has a rectangular induction passage 10, one wall 12 of which is pivotally movable and has the profile of one-half of a venturi. FIG. la also shows that the opposite cooperating wall 14 is also formed with a mating profile of a portion of a venturi. The opening 10 thereby comprises a variable area, rectangular venturi in which the airflow varies in proportion to the opening movement of the one wall 12 of the induction passage.

The movable wall 12 is pivotally mounted at 15 on the carburetor body and has a fuel metering rod 16 that is tapered for cooperation with a main fuel metering jet 18. The jet is located in an aperture in sidewall 14 at approximately the throat or constricted section of the venturi. The carburetor body includes a fuel reservoir 20 with a passage 22 conducting fuel to the main metering jet 18; a conventional throttle valve 24 in the induction passage below the venturi to control the flow of air and fuel through the passage; and a spring returned, vacuum actuated diaphragm 26 connected to the space between the throttle valve and venturi for moving the venturi wall 12 as a function of changes in venturi vacuum upon movement of the vehicle accelerator pedal between idle and wide open throttle speed positions. It will be seen, therefore, that the air and fuel flow change proportionally with movements of the venturi wall. Further details of construction and operation of this particular carburetor are not given since they are believed to be unnecessary for an understanding of the invention.

Returning to FIG. 1, the cold enrichment device 28 of the invention in this case is attached to one end of the carburetor, and is shown more clearly in cross section in FIG. 2. FIG. 2 also illustrates schematically the carburetor induction passage 10 and the float bowl or fuel reservoir 20.

The cold enrichment device shown in FIG. 2 consists of a multi-piece, hollow casting 50 that is open at opposite ends 52 and 54. The casting defines hollow chambers 56 and 58 sealingly separated by a narrow portion 60 of the casting. The chamber 56 has three ports 62, 64 and 66 that project through the sidewall. The port 62 connects by a passage 68 to a port 70 in the carburetor induction passage 10 located just below the closed position of the throttle valve 24 so as always to be subject to engine intake manifold vacuum. The port 64 is connected by a passage 72 to a port 74 in the induction passage at a point located above the closed position of the throttle valve 24 so as to be subject to atmospheric pressure and to be a source of additional clean air for the cold enrichment device. Port 66 connects by a passage 76 to a tube 78 opening into the carburetor fuel reservoir. The additional fuel required by the cold enrichment device thus is inducted separately from the main source of fuel supply that supplies the carburetor requirements during normal engine running operation. A further passage 80 is formed in casting for conducting this fuel to the port 62, in a manner to be described.

The wall portion 82 defining a portion of passage also serves as a guide for an annular rib cage and valve body 84. The latter is mounted within the open end of chamber 56 against a shoulder 87 on the casting. More specifically, the cage 84 has a reduced diameter front portion 86 consisting of circumferentially spaced ribs 88 that slidably house a conically shaped spool type valve land 90. The rear portion of cage 84 includes a second valve body 92 that has a valve seat 94 formed at one end and openings 96 at the opposite end. The openings communicate with a passage 98 connected by a passage 100 to the fuel passage 80.

Slidably received within valve body 92 is a second conically faced valve land 102. The land is connected by first and second reduced diameter stern portions 104 and 106 to the first valve land 90.

The annular rib cage 84 has a central partition 108 that defines an orifice type valve opening area 110 for cooperation with the slightly lesser diameter stem portion 104 and the more reduced neck portion 106. These two diameters provide varying areas for the flow of fuel from the passage 98 to the ports 64 and 62 in chamber 56. The end portion 112 of rib cage 84 also constitutes a valve opening cooperating with the conical face of valve land 90 either to completely block communication of flow to port 62 or at other times to vary the flow as a degree of axial movement of the valve.

1 At the left hand end of the enrichment device, as seen in FIG. 2, a thermostatically responsive bimetallic coil spring 114 is housed in an annular hollow casting 116 secured to the end 54 of casting 50. More particularly, the inner end (not shown) of the spring coil is anchored to a stationary stub shaft 120 fixed to casting 116, as best seen in FIG. 3. The opposite end of coil 8 spring 114 is engaged in a slot in the upturned end 124 of a lever 126 that is pivotally mounted on the casting 116 at 127. The lower end 128 of lever 126 is loosely mounted within a box-like bracket 130 fixed to the end of a plunger or shaft 132 integral with the valve lands 102 and 90.

An air passage 134 is adapted to be connected to a tube leading from a conventional engine exhaust manifold heat stove to supply heated air at times to the spring coil as the engine warms. This will cause an expansion of the coil and counterclockwise rotation of lever 126 to move the spool valve lands to the right for purposes to be described. Likewise, cooling of the engine operating temperatures will cause a contraction of the spring coil 114 and a resultant clockwise rotation as seen in FIG. 2 for movement of plunger 132 towards the left.

The right-hand casting portion is closed at its end 52 by the annular flexible diaphragm member of a vacuum servo 141. Secured to the diaphragm at its central portion is a plunger 144 that extends sealingly through the stationary servo housing 146 and the connecting casting portion 60 into an annular recess 148 in the conical valve land 90. An enlarged guide and retaining end'portion 150 is slidably received within the recess to constitute a lost motion connection between the plunger 144 and the valve land 90. The housing 146 serves as a stop for the leftward movement of diaphragm 140, which is biased to that position by a compression spring 152. The spring is seated at its opposite end against a suitable retainer indicated schematically at 154.

A second thermostatically responsive bimetallic coil spring element 156 is enclosed within a hollow housing or shell 158 secured to the open end 52 of casting 50. This element in this case is responsive to ambient temperature conditions. More particularly, the coil spring 156 has the inner end (not shown) mounted on a stub shaft 160 projecting from the shell wall (FIG. 4). The opposite end of the coil is received in a slot in the upturned end 164 of a lever 166 mounted on a pivot 168 also mounted in the shell wall. In this case, loosely mounted on the pin 168 between a pair of washers 170 is a fast idle speed cam plate 172. The plate has a first elongated slot 174 that engages the shank portion of pin 168 and a second shorter elongated slot 176 that is engaged by the shank of a pin 178 mounted on the lever 166. The lower portion of plate 172 is provided with a number of receding steps 178 on one edge that are each adapted to cooperate individually with the end of the plunger 144 to limit its rightward movement as a function of ambient temperature conditions. A manifold vacuum passage 180 connects manifold vacuum to the chamber 58 defined within casting 158 to move diaphragm 140 and plunger 144 rightwardly against whichever step 178 is in the path of the plunger at that particular time. As ambient temperature increases, the rotation of lever 166 in a clockwise direction will raise the cam plate 172 to permit the plunger 144 to then engage the next succeeding step and move further to the right.

In operation, the parts shown in FIG. 2 are in the engine off, cranking position. The thermostatic coil spring 114 is shown in the coldest position in which it exerts the greatest leftward closing force on the valve land 102. The spool valve 179, therefore, is pulled to the left the maximum amount shutting the heated air orifice 182. The ambient temperature responsive coil spring 156 also is shown in its coldest position positioning the plate 172 downwardly to the lowest position so that the high cam step 184 is located opposite the end of plunger 144.

Spool valve land 90 is positioned so that the passage opening 1 12 interconnects air port 64 to manifold port 62. The valve reduced neck portion 106 provides the larger area orifice opening 110 through which cranking fuel admitted to passage 98 will flow.

When the engine is cranked for starting purposes the manifold vacuum at this time acting on diaphragm 140 is not great enough to overcome the force of spring 152. Accordingly, plunger 144 is not moved in this case by diaphragm 140. This initial manifold vacuum or cranking vacuum, however, in port 70 is sufficient to create a pressure differential across the opening 112 to draw clean air from port 64 into manifold vacuum port 62. Simultaneously, a pressure differential is caused across fuel orifice 110 causing the flow of additional fuel from the fuel conduit 78 through orifice 110 into the manifold vacuum port 62 where it flows to the induction passage through port 70. This results in a cranking air/fuel mixture that is overrich to provide the necessary fuel vapor for starting the engine.

As soon as the engine is started, the increased engine running vacuum acting on diaphragm 1 now pulls the plunger 144 to the right against the high cam stop 18 1. This immediately moves spool valve 179 to the right to open orifice 182. A pressure differential then is created 5 across the orifice permitting the flow of hot exhaust manifold heated air at near atmospheric pressure from conduit 134 into the coil spring chamber 116 and out through the orifice 182 to mix with the air from port 64 and fuel flow from passage 98 flowing into the mani- 10 fold. Also in this case, the rightward movement of plunger 144 will move the larger diameter stem portion 104 of the spool valve 179 into the fuel orifice opening 110 to decrease the orifice size. This will immediately decrease the quantity of additional fuel flowing from the reservoir and thereby lean out the cranking mixture to a less fast but faster than normal cold running idle speed mixture, assuming cold operation continues.

The spool valve 17% will continue to move to the right either as a function of the heating of the engine 20 temperature responsive spring coil 114 or responsive to increases in ambient temperature as reflected by the' coil spring 156 raising the fast idle cam plate 172 to thereby permit further rightward movement of plunger 144. It will be seen, therefore, that when the engine temperature reaches its normal operating level, the spool valve lands 102 and 911 will have moved to the right sufficient to completely close outlets 110 and 112 by the conical backside 186 of valve land 102 and the conical face of land 90 to thereby block off all flow of additional fuel and air into the manifold passage 68 and port '70. The cold enrichment device is thereby shut off.

It will also be seen that this will be accomplished regardless of the ambient temperature since there is a lost motion connection between the plunger 144 and the spool valve land 90.

It will be seen, therefore, that the invention provides a cold enrichment device to provide a supplemental mixture of air and fuel to the engine during engine cranking conditions where an overrich mixture is demanded; and during engine running conditions when it is desired to immediately lean the cranking mixture to a less rich mixture but richer than normal because of cold operating conditions to overcome the effects of cold engine friction and poor fuel vaporization. it will be seen that the above is all accomplished proportional to engine and ambient temperatures.

It will further be seen that the engine provides good cold weather accelerations because when the manifold vacuum decays to a low level in the ambient temperature chamber 182, the spring 152 will force the spool valve 179 to the left to thereby open the valve in proportion to the vacuum decay below the spring preload force and provide additional fuel by presenting the smaller neck portion 106 of the valve in the fuel orifice 110. The system, therefore, responds to carburetor airflow and manifold vacuums to meter the added fuel flow accurately during these times.

While the invention has been described and illustrated in its preferred embodiment, it will be clear to those skilled in the arts to which it pertains that many changes and modifications may be made thereto without departing from the scope of the invention. For example, it will be clear that a symmetrical spool land 65 could be substituted for the conically faced land 90 of the spool valve; in this case, no pressure differential would act on the valve as it does in the preferred embodiment, where there is a tendency for the valve to quickly shut when it approaches the closing position.

We claim:

1. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle vai a mounted for a rotative movement across the passage between closed and fully open positions to control flow thro the passage, and a fuel reservoir, the device incln 3, control means to supply an air/fuel mixture to the :arburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising;

first conduit means connecting fuel from the reservoir and air to a port in the induction passage located at a point below the closed position of the throttle valve and subject. to engine vacuum,

first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at ,a predetermined level to subsequent posit ns progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and

vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direc ion to decrease the supplemental fuel and airflow,

second temperature responsive means operably connected to the servo means for controlling the movement of the servo means as a function of temperature changes,

the second temperature responsive means being responsive to ambient temperature changes from a predetermined level.

2. An enrichment device as in claim 1, wherein the valve means includes means responsive to changes in engine operating temperatures from a predetermined level for moving the valve means.

3. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle valve mounted for a rotative movement across the passage between closed and fully open positions to control flow through the passage, and a fuel reservoir, the device including control means to supply an air/fuel mixture to the carburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising;

first conduit means connecting fuel from the reservoir and air to a port in the induction passage lo cated at a point below the closed position of the throttle valve and subject to engine vacuum,

first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at a predetermined level to subsequent positions progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and

vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direction to decrease the supplemental fuel and airflow,

the temperature responsive valve means including means responsive to changes in engine operating temperature levels from a predetermined level for moving the valve means,

the last mentioned means comprising a bimetallic coil spring, the valve means comprising a spool valve having first and second spaced lands interconnected by a neck portion of reduced diameter, means connecting one end of the coil spring to the spool valve, second conduit means supplying engine exhaust manifold heated air to the first conduit means past the coil spring and spool valve lands, the first land blocking the flow of the heated air during engine vacuums lower than engine running levels and unblocking the flow upon movement of the valve in one direction, the movement of the valve in the one direction from the first land closed position moving the neck portion to restrict fuel flow from the reservoir, the second land variably controlling the flow of the heated air and fuel as well as additional airflow to the first conduit means, movement of the second land to one position completely blocking all flow to the first conduit means.

4. An enrichment device as in claim 3, wherein the servo means and spool valve are interconnected by a lost motion connection permitting a limited independent operation of each of the servo means and spool valve.

5. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle valve mounted for a rotative movement across the passage between closed and fully open positions to control flow through the passage, and a fuel reservoir, the device including control means to supply an air/fuel mixture to the carburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising;

first conduit means connecting fuel from the reservoir and air to a port in the induction passage located at a point below the closed position of the throttle valve and subject to engine vacuum,

first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at a predetermined level to subsequent positions progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and

vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direction to decrease the supplemental fuel and airflow,

second temperature responsive means operably connected to the servo means for controlling the movement of the servo means as a function of temperature changes,

the second temperature responsive means comprises a bimetallic spring coil responsive to changes in ambient temperature conditions from a predetermined level, and further means connected to the coil for movement therewith variably into the path of movement of the servo means to variably restrict the movement of the servo means and valve means as a function of the temperature.

6. An enrichment device as in claim 5, wherein the further means comprises a member having a stepped face, the servo means having a plunger connected to the valve means by a lost motion connection and projecting towards the steps of the stepped face for individual engagement therewith, spring means biasing the plunger towards the valve means, the steps being of progressively greater axial depth relative to the axis of the plunger, the movement of the coil in response to temperature changes progressively presenting the steps for engagement by the plunger to vary and limit its movement and thereby vary the position of the valve means. 

1. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle valve mounted for a rotative movement across the passage between closed and fully open positions to control flow through the passage, and a fuel reservoir, the device including control means to supply an air/fuel mixture to the carburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising; first conduit means connecting fuel from the reservoir and air to a port in the induction passage located at a point below the closed position of the throttle valve and subject to engine vacuum, first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at a predetermined level to subsequent positions progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direction to decrease the supplemental fuel and airflow, seCond temperature responsive means operably connected to the servo means for controlling the movement of the servo means as a function of temperature changes, the second temperature responsive means being responsive to ambient temperature changes from a predetermined level.
 2. An enrichment device as in claim 1, wherein the valve means includes means responsive to changes in engine operating temperatures from a predetermined level for moving the valve means.
 3. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle valve mounted for a rotative movement across the passage between closed and fully open positions to control flow through the passage, and a fuel reservoir, the device including control means to supply an air/fuel mixture to the carburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising; first conduit means connecting fuel from the reservoir and air to a port in the induction passage located at a point below the closed position of the throttle valve and subject to engine vacuum, first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at a predetermined level to subsequent positions progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direction to decrease the supplemental fuel and airflow, the temperature responsive valve means including means responsive to changes in engine operating temperature levels from a predetermined level for moving the valve means, the last mentioned means comprising a bimetallic coil spring, the valve means comprising a spool valve having first and second spaced lands interconnected by a neck portion of reduced diameter, means connecting one end of the coil spring to the spool valve, second conduit means supplying engine exhaust manifold heated air to the first conduit means past the coil spring and spool valve lands, the first land blocking the flow of the heated air during engine vacuums lower than engine running levels and unblocking the flow upon movement of the valve in one direction, the movement of the valve in the one direction from the first land closed position moving the neck portion to restrict fuel flow from the reservoir, the second land variably controlling the flow of the heated air and fuel as well as additional airflow to the first conduit means, movement of the second land to one position completely blocking all flow to the first conduit means.
 4. An enrichment device as in claim 3, wherein the servo means and spool valve are interconnected by a lost motion connection permitting a limited independent operation of each of the servo means and spool valve.
 5. An air/fuel mixture enrichment device for use with a carburetor having an induction passage open to air essentially at atmospheric pressure at one end and adapted to be connected to an internal combustion engine intake manifold at the opposite end, a throttle valve mounted for a rotative movement across the passage between closed and fully open positions to control flow through the passage, and a fuel reservoir, the device including control means to supply an air/fuel mixture to the carburetor during cold weather engine cranking and running operations that is supplemental to the carburetor normal air/fuel mixture supply, the control means comprising; first conduit means connecting fuel from the reservoir and air to a port in the induction passage located at a point below the closed position of the throttlE valve and subject to engine vacuum, first temperature responsive valve means variably movable from a first position closing the conduit means when the temperature is at a predetermined level to subsequent positions progressively opening wider the conduit means when the temperature progressively decreases below the predetermined level, and vacuum servo means responsive to the engine vacuum attaining an engine running level and acting thereon for moving the valve means at times in a closing direction to decrease the supplemental fuel and airflow, second temperature responsive means operably connected to the servo means for controlling the movement of the servo means as a function of temperature changes, the second temperature responsive means comprises a bimetallic spring coil responsive to changes in ambient temperature conditions from a predetermined level, and further means connected to the coil for movement therewith variably into the path of movement of the servo means to variably restrict the movement of the servo means and valve means as a function of the temperature.
 6. An enrichment device as in claim 5, wherein the further means comprises a member having a stepped face, the servo means having a plunger connected to the valve means by a lost motion connection and projecting towards the steps of the stepped face for individual engagement therewith, spring means biasing the plunger towards the valve means, the steps being of progressively greater axial depth relative to the axis of the plunger, the movement of the coil in response to temperature changes progressively presenting the steps for engagement by the plunger to vary and limit its movement and thereby vary the position of the valve means. 